use transform safe offsetX instead of clientX

[benbenbenbenbenben]

clientX is not desirable for two reasons.

1. if a css transform is applied, the coordinates may not be correct
2. clientX needs to take the element position into account to calculate a relative position

offsetX/Y avoids both of these problems

[lavrton]

Can you create an example where this update make sense?

[benbenbenbenbenben]

It makes sense in all situations because it is always easier to use the real values directly. That said, off the top of my head try this:

<div style='transform:scale(0.76)'>
    <div id='konvaContainer'></div>
</div>

Your calculated positions will always be wrong.

[lavrton]

I agree. Thanks for good PR.